The present invention relates generally to the control of arc effluent from an electrical arc-extinguishing assembly (e.g., arc chute) typically used in electrical circuit protective devices such as circuit breakers, particularly industrial circuit breakers which require effective means for extinguishing both ac and dc electrical arcs. An industrial circuit breaker for ac or dc applications, however, is only one type of electrical device that would benefit from the present invention. Other types of electrical devices, such as; residential circuit breakers, commercial circuit breakers, current limiting circuit breakers, magnetic-only circuit breakers, double-break rotary circuit breakers, contactors, relays, switches, safety disconnects, motor starters, current limiting units, or any electrical device involving the creation, control and exhaust of electrical arc effluent, would benefit from the present invention, which has the primary function of controlling the exhaust effluent resulting from the generation of an electrical arc.
A primary function of an electrical circuit breaker is to disconnect a protected circuit from the power source when the electrical contacts are opened and there is an electrical arc drawn between the contacts. One such arcing condition occurs when there is a short circuit overcurrent, where the impedance of the load in the protected circuit is inadvertently bypassed or "shorted out", thereby permitting an abnormal excess of current to flow in the circuit breaker. Upon the occurrence of this short circuit overcurrent condition, a current sensing unit (e.g., trip unit) within the circuit breaker detects the overcurrent condition and signals the circuit breaker to open a set of electrical contacts to effectively disconnect the protected circuit from the power source. An operating mechanism within the circuit breaker operatively connects the current sensing unit to the electrical contacts for operating the electrical contacts from the closed position to the open position when a pre-established trip threshold is detected by the current sensing unit.
Upon the occurrence of a short circuit overcurrent, the rapid response of the trip unit and operating mechanism results in the rapid parting of the electrical contacts. However, due to the inductive nature of the power source and protected circuit, and the high rate of rise of the short circuit overcurrent, the overcurrent is not immediately extinguished. Instead, an electrical arc is drawn between and support by the parting contacts. As the electrical contacts continue to separate under the opening action of the operating mechanism, the electrical arc is lengthened and drawn into an arc chamber within the circuit breaker, whereby an arc extinguishing assembly is used to control and extinguish the electrical arc, thereby disconnecting the protected circuit from the power source. Within the arc extinguishing assembly is an arc exhaust baffle which effectively controls the arc effluent that is exhausted outside of the circuit breaker arc chamber.
Some industrial circuit breakers have short circuit withstand ratings, which is the ability of a circuit breaker to stay closed on a short circuit fault for a pre-established period of time without tripping or self-destructing. Due to the purposeful delay in the opening action of the circuit breaker contacts under a withstand condition, high peak let-through currents occur, which generally heats up the electrical conductors before the contacts open, thereby reducing the effectiveness of the contacts and associated electrical conductors to act as thermal conductors to extract heat from the arc once it is drawn. The short circuit withstand function of an industrial circuit breaker is generally employed on upstream circuit breakers which feed and protect multiple down stream circuits, thereby providing a downstream circuit breaker, which may be closer to the short circuit fault, with the first opportunity to clear the fault without inadvertently disconnecting large portions of a protected electrical distribution network.
Other industrial circuit breakers have no short circuit withstand ratings and are generally called upon to open the electrical contacts as quickly as possible when a short circuit trip condition occurs. Under this situation, the well known phenomena of asymmetrical current waveforms in a short circuit fault may result in the generation of higher powered electrical arcs than would occur if the short circuit fault current were symmetrical. Current limiting circuit breakers having "blow open" contact arms generally fall under this category of industrial circuit breakers.
Whether the circuit breaker has short circuit withstand ratings or not, the short circuit let through current (i.e., the electric current that flows in the circuit breaker upon the occurrence of a short circuit fault) can be of significant magnitude, resulting in an electrical arc (ac or dc depending on the application) which must be controlled and extinguished by the arc chute in the arc chamber of the circuit breaker, and arc effluent which must be controllably exhausted to the external surroundings.
Electrical arcs and arc effluent are not new to the circuit protective devices industry, and circuit breakers have successfully controlled them using large arc chutes having steel arc plates to magnetically attract the arc, break the arc up into arclets producing a plurality of anode-cathode drops, and ultimately extinguishing the arc and exhausting the arc effluent through sizable vent ports to the environment external of the circuit breaker, thereby disconnecting the protected circuit from the power source. However, such arc extinguishing assemblies typically employ vent baffles having vent openings of a fixed geometry that are called upon to work effectively at both low and high short circuit interruption levels. However, as the short circuit interruption levels increase, so the internal pressure of the arc chamber increases, but the cross-sectional area of the vent openings remain fixed, thereby limiting the efficient exhausting of arc effluent at high short circuit interruption levels.
Thus, it would be beneficial to have an arc extinguishing assembly that overcomes the shortcomings of a vent baffle having openings that are fixed in cross-sectional area. It would also be beneficial to have a vent baffle that has geometric symmetry about multiple planes for enhanced ease of assembly. Such an arc extinguishing assembly would be beneficial in standard type circuit breakers having a single contact gap, rotary type circuit breakers having more than one contact gap, other electrical circuit protective devices having an arc-extinguishing function, or any electrical device involving the creation, control, and extinguishing of an electrical arc and the exhausting of arc effluent.